Using an uplink grant as trigger of first or second type of CQI report

ABSTRACT

Channel state feedback is provided from a UE to a base station as a first, detailed or a second, less detailed type of channel state feedback information. Initially it is determined whether the UE has received an uplink grant from the base station or not. If the UE has received an uplink grant, a first type of channel state feedback information is transmitted to the base station on the granted resource. If, however, the UE has not received an uplink grant, a second type of channel state feedback information is transmitted to the base station. Different types of channel state feedback information enables a UE and an associated base station to use available resources more efficiently, when requesting for and delivering channel state feedback information.

TECHNICAL FIELD

The present invention relates generally to a method and arrangement forproviding channel state feedback from a user equipment to a basestation, and especially for making more efficient use of availableresources when delivering channel state feedback.

BACKGROUND

Recent increase of mobile data usage and emergence of new applicationssuch as gaming, mobile TV and streaming content have motivated the 3GGeneration Partnership Project (3GPP) to work on the Long-Term Evolution(LTE) in order to ensure 3GPP's competitive edge over other, competitivecellular technologies.

LTE has been set aggressive performance requirements which rely onphysical layer technologies, such as Orthogonal Frequency DivisionMultiplexing (OFDM) and Multiple-Input Multiple-Output (MIMO) systems toachieve these targets. Some main objectives of LTE are to minimize thesystem and User Equipment (UE) complexities, to allow flexible spectrumdeployment in existing or new frequency spectrum, and to enableco-existence with other 3GPP Radio Access technologies (RATS).

In the LTE concept defined in the ongoing 3GPP work on standardization,the downlink will support fast channel dependent scheduling in both thetime and frequency domains. A conventional downlink scheduling conceptaccording to the prior art, may be described with stages 1:1-1:4, asillustrated in FIG. 1. A base station 100, which is referred to as anenhanced NodeB, or eNodeB in LTE, communicating with a UE 101, transmitsreference signals to UE 101 in a first stage 1:1. The reference signalscan be used by UE 101 to determine the present downlink channel quality.After having determined the downlink channel quality on the basis of thereceived reference signals, UE 101 sends one or more channel statefeedback reports, which in this context typically are represented byChannel Quality Indication (CQI) reports, back to eNodeB 100 in a secondstage 1:2. In eNodeB 100, the content of the one or more CQI reports canbe retrieved and used by a scheduler (not shown), to perform resourceallocation. UE 101 is informed of the resource allocation in a nextstage 1:3, which is followed by transmission of downlink data over theallocated resource, as indicated with a final stage 1:4.

More on this issue can be found in “3G Evolution: HSPA and LTE forMobile Broadband” E. Dahlman, S. Parkvall, J. Sköld, P, Beming, AcademicPress, 2007.

In one embodiment proposed for the LTE, UEs will be capable oftransmitting different types of CQI reports, such as full CQI reports,partial CQI reports, and differential CQI reports. In this context, fullCQI reports are defined to cover the whole downlink transmissionbandwidth scheduled for a UE. Different full CQI reports may, however,have different frequency resolution and may also be filtered andprocessed in different ways. In addition, different full CQI reports maybe encoded in a variety of alternative ways. Partial CQI reports on theother hand cover only a part of the downlink transmission bandwidth. Thecovered part of a partial CQI report may be a set of contiguous, or aset of distributed resource blocks. Differential CQI reports may containan encoded version of the update vector relative to a previous CQIreport.

Furthermore, for CQI reports used together with different antennaconfigurations, such as SISO (Single-In Single-Out), MISO (Multiple-InSingle-Out), SIMO (Single-In Multiple-Out), or MIMO (Multiple-InMultiple-Out), transmission could also be different. For MIMO, a CQIreport may include information, such as e.g. transmission rank and/orpre-coding weights and/or other feedback parameters to be used by theeNodeB multiple antenna transmission scheme.

In one proposal for LTE presented in 3GPP, the UE may have a set ofrules that specifies the conditions for CQI reports to be transmitted.According to this proposal, each CQI transmission trigger is associatedwith a specific type of CQI report in such a way that when a triggeringcriteria is true, the UE transmits a CQI report of an associated type.This procedure is similar to how compressed mode is parameterized inWCDMA. For WCDMA compressed mode, each UE is provided with atransmission gap pattern set (TGPS) consisting of transmission gappatterns (TGP), each defining a transmission gap of a configurablelength that is used for a specific measurement purpose. CQI reports maybe specified in a similar way, wherein each UE has a CQI reportingtrigger set (CRTS), consisting of one or more CQI reporting triggers(CRT) that specify when a specific type of CQI report shall betransmitted.

FIG. 2 illustrates a table of a CQI trigger configuration for a UE,according to the prior art described above. The table comprises aplurality of CQI reporting triggers, CRT 1-n, configured for the UE.Each CRT is associated with one of the CQI report types, CQI A-X. Whenfor example the trigger criteria specified by CRT 1 is true, a reporttype defined by CQI A will be transmitted from the UE to an eNodeB, asindicated in the table.

A CRT is typically expressed in terms of a logical expression which mayinvolve one of, or a combination of, timers, events, and conditions,consisting of logical statements such as AND, OR, NOT, WHEN, and/or IF.A simple periodic CQI reporting trigger may consist of just a periodictimer and a rule that a certain CQI report shall be transmitted everytime the timer expires. In another exemplified scenario, a simple eventbased CQI reporting trigger may configured to state that a certain typeof CQI report shall be transmitted every time the triggering event, suchas e.g. a handover event, occurs. A condition that could be included inthe decision to transmit a certain CQI report or not, is e.g. if thedownlink activity is above a specified threshold.

CQI reports may also be transmitted in different ways. A CQI reportcould be transmitted on a dedicated control channel resource, or on ascheduled resource provided on a shared channel. CQI reports may occurat known time instances and use a format known to the eNodeB, or theoccurrence and format may be more dynamic. In the latter case the MACheader typically needs to include information about how the CQI reportwas transmitted, or else the eNodeB may have to perform blind detectionon the CQI transmission format.

What types of CQI reports a UE shall use, and what criteria that willtrigger them, are typically set-up by higher layer signaling, e.g. RRCsignaling. In addition to configuring rules, defining when and how CQIreports are to be transmitted, the eNodeB also have the option toexplicitly request for CQI reports on demand, typically by using RRCsignaling.

The LTE uplink is based on single-carrier modulation and uses frequency,time and code division multiple access principles (FDMA, TDMA and CDMA).The LTE uplink consists of physical uplink control channels and datachannels that are orthogonally frequency multiplexed. The single-carrierproperty of the LTE uplink makes it impossible for a UE to transmit on aphysical control channel and a physical data channel in the sametransmission-time-interval (TTI). Hence, if a UE is transmitting data ona physical data channel, the control information that must be sent inthe same TTI must also be sent on the physical data channel. The UE willuse the physical control channel to transmit control signaling only inthe case when the UE has no data transmission, and, hence is not usingthe physical data channel.

There are at least three types of control signaling that may be sentin-band on the physical data channel in case the UE has uplink data totransmit, namely Hybrid ARQ (HARQ) ACK/NACK feedback for downlink datatransmissions, scheduling requests and CQI reports.

The current assumption in 3GPP regarding the HARQ feedback and thescheduling request is that the HARQ will consist of one bit per MIMOstream, while the scheduling request might consist of just a single bit,indicating if a UE has data it wants to transmit or not.

The CQI reports on the other hand can be significantly larger. Theamount of bits that can be spent on the CQI reporting may depend on anumber of different criteria, such as: downlink transmission mode, e.g.SISO or MIMO; type of downlink traffic, e.g. VoIP or Web; downlink radiocharacteristics, e.g. coherence time and/or coherence bandwidth; currentuplink load and/or current downlink activity. Furthermore, while theHARQ feedback and the scheduling request signaling are vital for thecommunication protocols to work at all, the CQI reports can be seen moreas performance enhancing feature for the downlink.

The more uplink resources that are spent on CQI reports, the better linkadaptation and scheduling decisions can be made, and the better theperformance of the downlink may be achieved. As for signaling ingeneral, there is, however, a trade-off between the amount of resourcesthat are used for signaling and the amount of resources available fortransmission of user plane data traffic. In current state-of-the-art itis known that it is beneficial to adapt the CQI reporting scheme to theconditions listed above.

A drawback with prior art CQI reporting mechanisms is, however, the lackof flexibility as to the use of available resources.

In order to fully support all possible CQI feedback schemes in allpossible scenarios one would need to allocate an unreasonable amount ofphysical resources for uplink physical control signaling.

Even with a limited number of schemes applied, new feedback schemes aredifficult to introduce, especially if they require that the uplinkphysical control channels need to be re-designed.

SUMMARY

The present invention aims to solve at least some of the problemsmentioned above by providing a more efficient use of the uplink physicalcontrol channel.

The present invention relates to a method for triggering of a CQIreporting transmission from a UE. More specifically, the inventionrelates to a method in a user equipment, UE, for providing channel statefeedback from the UE to a base station, using one of two different typesof information, wherein the second type of information is less detailedthan the first type.

Initially, it is determined whether the UE has received an uplink grantfrom the base station or not. If the UE has received an uplink grant, afirst type of channel state feedback information is transmitted to thebase station on the granted resource. If, however, the UE has notreceived an uplink grant, a second type of channel state feedbackinformation is instead transmitted on a dedicated resource, or nochannel state feedback information is transmitted at all. Hereby, theuplink physical control channel can be more efficiently dimensionedsince only less detailed channel state feedback information in a formatcomprising very few bits is transmitted on this channel. Suchinformation could for example comprise the selection of a specificantenna from an antenna array. More detailed channel state feedbackinformation in a format comprising a large number of bits is transmittedon the granted resource. Such information could for example comprisefrequency information on resource block level.

Thus, the invention limits the amount of overhead that must be allocatedin a “dedicated” way for channel state feedback, while still allowingdetailed feedback to be transmitted on a scheduled resource. Without thepresent invention these dedicated resources would need to be dimensionedto handle worst case CQI reporting demand, including possible MIMOrequirements. Moreover, the reserved physical control channel resourceswould be wasted if the UE transmitted uplink data, since the uplinkcontrol signaling would then be transmitted using the scheduled resourceinstead and the reserved resources would not be used. By implementingthe suggested mechanism, the uplink control channel can instead beconfigured to a minimum requirement.

According to one aspect of the invention, a UE receiving a grant when ithas no uplink data to transmit, sends channel state feedback, such as aCQI report on the granted resource, even if no other condition thatnormally triggers a CQI report transmission is valid. As a consequence,the base station may interpret a scheduled uplink transmission that onlyconsists of channel statement feedback, such as a CQI report, as animplicit signaling of an empty buffer status information message and/oras an acknowledgement on the uplink grant message that was transmittedin the downlink.

In addition, by introducing the proposed channel state feedbacktriggering procedure we can avoid sending unnecessary CQI reports,thereby saving control channel resources.

Another embodiment further comprises the step of only transmitting thechannel state feedback information if the channel state feedback triggercriteria specified for the UE is found to be valid.

According to yet another embodiment, the less detailed type of channelstate feedback information is periodically transmitted if the UE has nouplink grant, while the more detailed, first type of channel statefeedback information is periodically transmitted if the UE does have anuplink grant.

According to another embodiment, two alternative ways of transmittingchannel state feedback information of the first type is provided.According to this embodiment, both presence of an uplink grant anduplink data is considered. If the UE has uplink data and an uplinkgrant, a scheduled uplink transmission will consist of both channelstate feedback information and uplink data. If, however, no uplink datais present, a scheduled uplink transmission will consist of only channelstate feedback information. Scheduled uplink transmission according toany of the described embodiments may be utilized as a signaling of anempty buffer status information to the base station, or as anacknowledgement of an uplink grant that has been transmitted in thedownlink.

According to yet another embodiment, the report to be used fortransmission of the respective channel state feedback information may bedependant on the size of the received uplink grant, i.e. a base stationmay be able to select the size of a requested channel state feedbackreport by varying the uplink grant size, and the UE will be able torecognize the size as an indication as to which amount of informationthat is required by the base station. In addition, such a mechanism willoffer an alternative to blind detection, since the base station knowswhat channel state feedback information format to expect. According tothe suggested embodiment, the size of the uplink grant received at a UEis compared to a threshold, T1 channel state feedback information isprepared and transmitted in a report of a first type, having a sizeassociated with T1 only if the uplink grant size exceeds T1. Such acomparison may also be gradually repeated for one or more thresholds, T2. . . Tn, wherein T1>T2 . . . >Tn, and wherein each threshold isassociated with a specific report type. The size of the uplink grant maybe defined to represent an indication of the bandwidth, the modulationsize, and/or the code rate associated with the uplink grant.

Alternatively, the remaining available energy for data transmission maybe included on the uplink as a condition for transmission of the channelstate feedback information.

According to another aspect, a UE for providing channel state feedbackfrom the UE to a base station is presented, comprising a determiningunit for determining whether the UE has received an uplink grant fromthe base station or not. The UE also comprises a transmitting unit fortransmitting a first type of channel state feedback information to thebase station on the granted resource if the UE has received an uplinkgrant, or a second type of channel state feedback information on adedicated resource if no uplink grant has been received. Alternatively,no channel state feedback information at all is transmitted in thelatter scenario, i.e. channel state feedback is only transmitted inresponse to a received uplink grant.

In another embodiment, the determining unit may be further adapted todetermine whether relevant channel state feedback trigger criteriaspecified for said UE is valid or not. According to this embodiment,channel state feedback information is only transmitted if also thechannel state feedback trigger criteria is found to be valid.

The channel state feedback information is typically transmitted in areport generated by a generating unit.

According to yet another embodiment, the generating unit may be adaptedto periodically generate a second, less detailed report type if the UEhas no uplink grant, while a second, more detailed report type isinstead generated if the UE does have an uplink grant.

According to another, alternative embodiment, the determining unit maybe adapted to compare the size of a dynamic uplink grant to a threshold,T1, and to generate a report associated with T1, if the size of theuplink grant exceeds T1. The determining unit may also be adapted togradually repeat such a procedure for one or more thresholds asdescribed above. If a report is required for all occasions, the smallestthreshold may be set to 0.

In one embodiment, the determining unit may also be adapted to includeremaining available energy for data transmission on the uplink as acondition for generating a channel state feedback report.

According to yet another aspect, a method in a base station, comprisinga scheduler is provided for obtaining channel state feedback from a UE.According to one aspect of the invention, it is the presence of downlinkdata in the base station that triggers the scheduler to provide anuplink grant to the UE in order to receive the downlink channel statefeedback required for link adaptation and/or channel dependentscheduling of downlink data to that UE on the granted resource. Thus, incase the base station needs channel state feedback information althoughthere is no ongoing uplink transmission, an uplink grant can be sentfrom the base station to obtain the information. If the scheduler hasdetermined that channel state feedback is required, an uplink grant isgenerated, and the uplink grant is provided to the UE in order toreceive the channel state feedback on the granted resource.

According to another embodiment, it is also determined whether downlinkdata is present in the base station or not, and if this is the case, anuplink grant is generated and provided to the UE, in order to receivedownlink channel state feedback on the granted resource.

According to yet another embodiment, the load of the uplink isconsidered, determining at the base station whether the uplink load isbelow a threshold, th or not. If this is the case, an uplink grant isgenerated and provided to the UE. Otherwise, the signaling required forproviding channel state feedback information is avoided in favor ofongoing traffic.

An uplink grant may be provided to the UE for the purpose of receivingan uplink transmission on the granted resource, containing at leastchannel state feedback. The retrieved uplink transmission may then beused by the base station to estimate the uplink channel quality for linkadaptation and/or channel dependent scheduling of uplink data from theUE. Hereby, the use of both uplink probing and non-scheduled CQI reportscan be limited. The scheduler can thus place the channel state feedbackreports on resources where it wants to probe the uplink channel.Alternatively, the uplink grant may be provided to the UE for thepurpose of maintaining uplink synchronization.

According to yet another aspect, a base station, comprising a scheduleradapted to obtain channel state feedback from a UE is provided. Thescheduler comprises a generating unit, adapted to determine whetherchannel state feedback is required or not, and, in case channel statefeedback is required, the generating unit is further adapted to generatean uplink grant in order to receive channel state feedback from the UEon the granted resource. The uplink grant is then transmitted by atransmitting unit, and a receiving unit is adapted to receive channelstate feedback in response to the transmitted uplink grant.

According to one alternative embodiment, the generating unit is adaptedto provide an uplink grant to the UE in order to receive downlinkchannel state feedback required for link adaptation and/or channeldependent scheduling of downlink data to the UE on the granted resourceif it is found that the base station has downlink data.

According to another embodiment, the generating unit is adapted toprovide an uplink grant to the UE if it is found that the uplink load atthe UE is below a specific threshold, th. The threshold is typicallyadapted such that uplink data from other UEs will not be negativelyaffected.

According to yet another embodiment, the generating unit may be adaptedto provide a UE with an uplink grant for the purpose of receiving anuplink transmission on the granted resource, wherein the uplinktransmission comprises at least channel state feedback. The schedulermay also be adapted to use the uplink transmission to estimate theuplink channel quality for link adaptation and/or channel dependentscheduling of uplink data from the UE.

The generating unit may be adapted to provide a UE with an uplink grantfor the purpose of maintaining uplink synchronization. Alternatively,the generating unit may be adapted to generate an uplink grant ofvariable size, enabling the base station to request for channel statefeedback information of a variable size.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described in more detail by means ofexemplary embodiments and with reference to the accompanying drawings,in which:

FIG. 1 is a basic overview of a signalling procedure between a userequipment and an eNodeB, according to the prior art.

FIG. 2 is a table indicating a configuration of CQI report triggers,according to the prior art.

FIG. 3 is a flow chart illustrating a procedure for providing a CQIreport from a user equipment to an eNodeB, according to the prior art.

FIG. 4 a is a flow chart illustrating a procedure for selecting a CQIreport in user equipment, according to one embodiment.

FIG. 4 b is a flow chart illustrating a procedure for selecting a CQIreport in a user equipment, according to another embodiment.

FIG. 5 is a flow chart illustrating a procedure for selecting a CQIreport in a user equipment, according to yet another embodiment.

FIG. 6 is a flow chart illustrating a procedure for selecting a CQIreport in a user equipment, according to another alternative embodiment.

FIG. 7 is a block diagram, schematically illustrating an eNodeB, adaptedto request for a CQI report, according to any of the describedembodiments.

FIG. 8 is a block diagram, schematically illustrating a UE, adapted toprovide a CQI report to a base station, according to any of thedescribed embodiments.

FIG. 9 is a flow chart illustrating a procedure for an eNodeB requestinga CQI report from a UE, according to one embodiment.

FIG. 10 is a flow chart illustrating a procedure for an eNodeBrequesting for a CQI report from a UE, according to another embodiment.

DETAILED DESCRIPTION

Briefly described, the present invention involves a method, a userequipment and a base station adapted to handle channel state feedbackreports in a more flexible way. More specifically, a channel statefeedback procedure is provided which utilises the resources availablefor transmission of channel state feedback more efficiently. This isachieved by including uplink grant availability into the channel statefeedback reporting triggers used for determining when and how to sendchannel state feedback from a UE, i.e. a channel state feedbackreporting rule is set-up at the UE, specifying that the channel statefeedback reporting will rely on whether a respective UE has obtained anuplink grant or not. Alternatively, uplink grant availability isconfigured to be the only trigger, specifying which type of channelstate feedback report to transmit. By using an uplink grant, alone or incombination with other channel state feedback trigger criteria, a basestation will also be able go get more out of using channel statefeedback reports than what is possible with prior art solutions.

In the following exemplified embodiments, channel state feedback reportsdelivered from UEs will consequently be referred to as CQI reports andbase stations will be referred to as enhanced LTE base stations, i.e.eNodeBs. Furthermore, the channel state feedback rules, specifying whento transmit a CQI report, which may be expressed in terms of a logicalexpression involving one or a combination of timers, events and/orconditions, will be referred to as CQI reporting triggers. It is,however, to be understood that the described embodiments may beapplicable also for other comparable channel state feedbackimplementations.

FIG. 3 is a simplified flow chart illustrating a procedure for providingchannel state feedback in the form of CQI reports from a UE to aneNodeB, according to the prior art. In a first step 300, the criteriafor when and how to deliver different types of CQI reports, typicallydefined as specified above with reference to FIG. 2, configured as aCRTS by eNodeB, is delivered to and received by the UE. In a next step301, a continuous checking procedure, for determining whether the CRTcriteria specified by the CRTS is fulfilled, is initiated. If thecriteria of a CRT is found to be fulfilled in a step 302, a CQI reportof the respective type will be transmitted by the UE, as illustratedwith a final step 303. If, however, the CRT criteria is not fulfilled,the checking procedure is repeated starting again with step 301. Ifthere are a plurality of different types of CQI reports configured forthe UE, the checking procedure will be repeated accordingly for eachreport type. Obviously, such a procedure for deciding when to transmitCQI reports leaves no room for flexibility as to the use of availableresources or as to what information that can be retrieved from a CQIreport.

Accurate channel quality knowledge at the eNodeB is mainly required whendata is transmitted in the downlink. When there is no downlink datatransmission taking place, there is, however, no or very small need fordetailed CQI reports. Furthermore, when the UE is receiving data in thedownlink, there will typically also be transmission activity in theuplink, and, thus, CQI reports should preferably be sent mainly when theUE is anyway transmitting in the uplink in response to downlinktransmissions, as this will minimize the amount of semi-staticallyallocated CQI resources. For this reason, the CQI overhead can bereduced by defining two different CQI formats, wherein a first formatusing a larger number of bits, is used in situations when the UE wouldtransmit data in the uplink anyway, while a second format using asmaller number of bits is used for CQI transmission only. Since thetransmission structure is different for the two transmission cases,having different sizes for the two CQI reporting formats, such aprocedure will not complicate the overall structure.

According to one embodiment, two different types of CQI reports,specified as a low-resolution type, i.e. a coarse type, and as ahigh-resolution type, i.e. a detailed type, respectively, are specifiedand the CQI reporting trigger criteria associated with these two CQIreport types is set-up in such a way that if it is found that a UE hasreceived an uplink grant from an eNodeB during a CRT check, the UE willtransmit a detailed high-resolution CQI report using the grantedresource, while a coarse low-resolution CQI report will be transmittedon the dedicated uplink physical control channel, if no uplink grant hasbeen received. A method of managing CQI report delivery according tothis embodiment will now be described in further detail with referenceto FIG. 4 a.

The first two steps 400, and 401 are executed in the same manner as forthe prior art described above, referring to FIG. 3. In a subsequent step403, however, it is determined if the UE has received an uplink grant ornot. The presence of an uplink grant at the UE is unconditionallyinterpreted by the UE as an indication that a CQI report of a first type(type 1) is to be transmitted to the eNodeB on the granted resource.Such a transmission, which may comprise both data and channel statefeedback information, is transmitted in a step 404. If, however, nouplink grant is present at the UE, a CQI report of a second type (type2), comprising only channel state feedback information is to betransmitted on a dedicated resource, as indicated in another step 405.Alternatively, the type 2 CQI report alternative may be configured toinstruct the UE to not transmit any CQI report at all, i.e. a CQI reportis only transmitted to the eNodeB of an uplink grant is present at theUE.

According to another embodiment, which will be described with referenceto FIG. 4 b, also other trigger criteria, defined as CRT criteria, isconsidered when determining what type of CQI report to transmit from theUE. The CRT criteria may e.g. be based on the time since the lasttransmission of a CQI report took place and/or whether the presentdownlink activity exceeds a predefined threshold or not.

In FIG. 4 b, steps 400 and 401 are equivalent to the ones already shownin FIGS. 3 and 4 a. In a next step 402, however, the relevant CRTcriteria is checked. If the CRT criteria is not valid, no CQI report istransmitted, and the checking procedure is restarted at step 401. If, onthe other hand, the CRT criteria is found to be valid, it is determinedif an uplink grant is present at the UE in a next step 403. If an uplinkgrant is not present, a coarse CQI report of type 2 is transmitted in astep 404, while a more detailed report of type 1 is instead transmittedin another step 405 if an uplink grant is present at the UE. Also inthis scenario, the type 2 report alternative may be configured toinstruct the UE to not transmit any CQI report at all.

Including uplink grant availability in the CQI reporting triggers haslarge implications on the practical usage of the CQI reports, since theCQI reports may be useful for a lot more purposes compared to what canbe achieved with other state of the art solutions. A scheduler of aneNodeB may for example grant a UE a specific resource for the purpose ofperforming uplink channel estimation, regardless if it has received ascheduling request from the UE or not. If the UE responds to the grantby transmitting a CQI report on the granted resource, the scheduler willbe provided with information about the uplink and downlink channelquality at the same time. Such a procedure may be used as a moreeffective alternative to channel sounding, where only a referencesignal, carrying no information is transmitted from the UE.

In the situation when a UE has an uplink grant but no uplink databuffered for transmission, a CQI type 2 report received by the eNodeB,implicitly indicates to the eNodeB that the UE has no uplink data, andas a consequence for the eNodeB, requesting for empty buffer statusinformation by the eNodeB will be superfluous, resulting in reducedsignaling.

The described channel state feedback procedure can enable the schedulerof an eNodeB, which typically consists of an uplink scheduling functionand a downlink scheduling function, to perform a trade-off betweenuplink and downlink capacity. If the downlink scheduling functionrequires a CQI report to be delivered, it can check with the uplinkscheduling function if the corresponding UE has an uplink grant or not.If the UE already has an uplink grant, the scheduler can expect a CQIreport to be transmitted on the granted resource. If, however, the UEdoes not have an uplink grant, the downlink scheduling function mayrequest the uplink scheduling function to schedule the correspondinguser in the near future, even if the corresponding user has not made anyscheduling request. If the uplink load is low, the uplink schedulingfunction may choose to give the user a grant just for the sake oftransmitting the CQI report that the downlink scheduling functionrequested. If, on the other hand, the present uplink load is high, i.e.higher than a specified threshold value, the uplink scheduling functionmay prioritize uplink data transmission from other users, and, thus, noresources will be used for CQI reporting as long as the uplink loadremains high.

Channel state feedback may also be used to keep uplink userssynchronized. The channel state feedback retrieved by the eNodeB inresponse to a received uplink grant may be used to control the load onthe uplink synchronization channel, allowing the eNodeB to gain directcontrol of which users to keep in synchronized state. For example, insituations with low load, the scheduler can choose to keep the userssynchronized for a relatively long time period in order to provide aquicker response time once new data arrives at the UE. Thus scheduledCQI reports may be used instead of synchronization probes on the uplinksynchronization channel.

In situations when the UE is power limited on the uplink it may not beable to transmit a CQI report and data in the same TTI. For coveragereasons it would then be beneficial to have the option to turn off CQIreporting in cases where it has been found that the energy left for datatransmission has fallen below a threshold. Therefore, also the remainingavailable energy for data transmission could be included in the CQIreporting trigger criteria. Since CQI reports and data transmissions aretime multiplexed on the uplink, the removal of the CQI reporting fromthe TTI will give a power limited UE more time to transmit the datasymbols, and hence the energy of the data part can be increased. TheeNodeB may interpret an absence of a CQI report that should have beenincluded according to one CTR as an indication that the power headroomof that UE is zero or below a minimum level. This option, thus can beused to avoid explicit signaling of the power headroom for severelypower limited UEs.

It is also possible to combine the suggested channel state feedbackprocedure with a rule that provides uplink grants implicitly, e.g. byassociating every downlink transmission with an implicitly granteduplink resource. An uplink resource grant may then be pre-configured insuch a way that every UE that is scheduled in the downlink can derive anuplink grant for a future uplink transmission. This implicit uplinkgrant may e.g. be based on the position of the downlink resourceallocation description on the downlink scheduling control channel. Sucha rule could be beneficial since we know that when there is downlinkdata to transmit to a UE, transmission of HARQ feedback, TCP feedback,and CQI reports in the uplink will be required. In one alternativeembodiment, a flag in the downlink assignment could be used to indicateif a downlink assignment is to be associated with an implicitly granteduplink resource or not.

Also the use of DRX/DTX, i.e. Discontinuous reception/Discontinuoustransmission, in the UE may affect the procedure for delivery of CQIreports. A UE operating in a DRX/DTX mode may fail to produce anexpected CQI report of a certain type since it is configured to notlisten to the downlink reference symbols all of the time. Thus, a CQItriggering criteria may also include information regarding whether theUE is in a certain DRX/DTX mode or not. A UE in DRX mode may e.g.transmit a snapshot CQI report, based on a single observation of thedownlink reference symbols, while a processed CQI report based onobservations of downlink reference symbols from several TTIs may insteadbe transmitted if the UE is not in DRX mode.

A CQI reporting rule according to the claimed invention can be set-upstating that if a UE obtains an uplink grant when the UE has no uplinkdata to transmit, it sends channel state feedback, such as a CQI reporton the granted resource, even if no other CRT criteria that normallytriggers a CQI report transmission is valid. As a consequence, theeNodeB may interpret a scheduled uplink transmission that only consistsof channel state feedback, such as a CQI report, as an implicitsignaling of an empty buffer status information message, and as anacknowledgement of the uplink grant that was transmitted in thedownlink.

An alternative procedure for managing CQI report delivery in a UEaccording to another embodiment will now be described with reference toFIG. 5. According to this embodiment, also presence or absence of uplinkdata in the UE is considered and two different type 1 CQI reports, i.e.detailed reports are introduced, namely a full type 1 CQI report,comprising only channel state feedback information, and a combined type1 CQI report, comprising a combination of uplink data and channel statefeedback information.

In resemblance to the previous embodiment, also this embodiment startswith the configuring of a CRTS of a UE, as illustrated with a first step500, followed by the initiation of a procedure for continuously checkingthe CRTs, specified by the CRTS in a next step 501, a checking of CRTcriteria in a step 502, and of an uplink grant in a subsequent step 503.In resemblance to the previous embodiment, no uplink grant in the UEresults in the transmission of a type 2 CQI report in a step 504. If,however, an uplink grant is found to be present in step 503, it isdetermined whether there is uplink data present in the UE in a next step505. Depending on whether uplink data is present in the UE or not, afull or a combined CQI report of type 1 will be chosen for transmissionof the channel state feedback information. Accordingly, no uplink datawill result in the transmission of a full type 1 CQI report in a step506. Such a detailed report may be configured to contain anything frome.g. 10% channel quality information, leaving remaining space empty, to100% channel quality information. If instead uplink data is present, acombined type 1 CQI report will be transmitted, as illustrated withanother step 507. Once a report has been delivered from the UE, the CRTchecking procedure is repeated, starting with step 501. If the eNodeBprovides the UE with an uplink grant according to the describedembodiment it will, however, not know if it is to expect a type 1 CQIreport or a type 2 CQI report since it does not know if the UE hasuplink data or not. The eNodeB therefore will have to perform blinddetection to determine whether a type 1 CQI report is a full or acombined version.

The introduction of an uplink grant of a dynamic size may enable theeNodeB to implicitly know the transmission format of received channelquality information and, thus, to provide a powerful alternative toblind detection. The use of such a dynamic uplink grant will now beillustrated in yet another embodiment with reference to FIG. 6. Also inFIG. 6, the initial steps, namely Steps 600-604 are basically performingthe same procedures as steps 500-504 in FIG. 5, wherein a CQI report oftype 2 is transmitted on a dedicated channel in step 604, if no uplinkgrant is present at the UE. If an uplink grant is present at the UE, thesize of the uplink grant will be considered in a step 605. In step 605,it is determined whether the size of that uplink grant exceeds a firstthreshold T1. If this is the case, a CQI report of type 1, having aspecific size, size 1, associated with the comparison step, istransmitted to eNodeB in a step 606. If, however, the size of the uplinkgrant is smaller than T1, the procedure may be repeated, wherein theuplink grant is gradually compared to smaller thresholds, T2 . . . Tn,where T1>T2> . . . >Tn, until a match is found, i.e. the size of theuplink grant is bigger than a threshold, and a CQI report correspondingto the respective comparison step is transmitted. A final comparison isillustrated with a step 607, which results in either the transmission ofa size n type 1 CQI report or no report at all. The smallest threshold,Tn may have a small amount or even be set to 0 if it is required that aCQI report is to be transmitted on each occasion when the CTR criteriahas been found to be valid.

A simplified block diagram of a base station, exemplified as an eNodeB,adapted to operate in accordance with at least the embodiments describedabove, will now be described with reference to FIG. 7. It is to beunderstood that, for simplicity reasons, units which are not necessaryfor the understanding of the claimed invention have been omitted. It isalso to be understood that all units mentioned in this document are tobe interpreted as exemplified logical units, which may be implemented assingle units of in combination with other units in any of variouspossible ways.

The eNodeB 700 comprises a scheduler 701, adapted to administratescheduling between the eNodeB and one or more UEs, represented here byUE 800. The scheduler 701, which typically includes separate uplink anddownlink scheduling functions (not shown), comprises a generating unit703, adapted to determine whether channel state feedback information isrequired or not according to predetermined rules configured for thescheduler 701, and to generate an uplink grant to be transmitted to theUE 800 when it is found that channel state feedback information isrequired. An uplink grant generated by the scheduler 701 is transmittedto the respective UE via a transmitting unit 704 of a transceiver 705,and channel state feedback, which may be transmitted to the eNodeB 700in response to the uplink grant, is received by a receiving unit 706 ofthe transceiver unit 705. Also rules for how to interpret theinformation retrieved from channel state feedback, or absence ofexpected channel state feedback, will be specified in the configurationof the scheduler.

Also a UE operating in accordance with at least the embodiment describedabove, will require modifications. A simplified block diagram of a UE,according to one embodiment, will now be described with reference toFIG. 8. Also in this figure, units and functions not necessary for theunderstanding of the claimed invention have been omitted. The UE 800communicating with an eNodeB 700, comprises a generating unit 801 forgenerating a CQI report when the specified criteria is found to bevalid, according to any of the embodiments described above. Thegenerating unit 801 further comprises a determining unit 802, adapted todetermine whether a respective CRT criteria is fulfilled or not, and,thus, whether a respective CQI report is to be transmitted or not.Obviously, the determining unit 802 is configured to determine whetheran uplink grant has been received by the receiving unit 804 of atransceiver unit 805 of UE 800 and is present at the UE or not. Thedetermining unit 802 also may determine whether the UE has uplink datato transmit or not. In addition, the determining unit may take the sizeof a received uplink grant into consideration when determining whichversion of channel state feedback information to transmit. The CQIreporting trigger criteria, specified for the UE in one or more CRTs806, is stored within, or in association with the generating unit 801.Once the availability of an uplink grant, and, if applicable, thevalidity of the remaining CRT criteria, has been determined by thedetermining unit 802, a CQI report is generated by the generating unit801. The chosen CQI report is then transmitted to the eNodeB 700 via atransmitting unit 807 of the transceiver unit 805.

The operating steps of an eNodeB according to one embodiment will now bedescribed with reference to FIG. 9, where scheduling is activated in afirst step 900. When it is determined by the scheduler of eNodeB that aCQI report is required in a next step 901, the scheduler generates anuplink grant in a step 904, and transmits an uplink grant to therespective UE in a final step 905. The scheduling then proceedsaccordingly, wherein the CQI report is awaited. In one alternative, thestep 901 may be represented by checking the condition whether downlinkdata is present or not, i.e. if downlink data for the respective UE ispresent at the eNodeB, an uplink grant is generated in step 904 andtransmitted in step 905, while no UL grant is transmitted otherwise.

An alternative embodiment of a configuration of the eNodeB is describedwith reference to FIG. 10, where the first step 900 and the final steps904 and 905 are the same as described in the previous embodiment. Instep 902, it is determined whether downlink data is present or not. Ifdownlink data is present, the uplink load of the eNodeB is compared to athreshold, th in a next step 903, and if the uplink load is found to bebelow that threshold, an uplink grant is generated in step 904, andtransmitted in step 905. If, however, the uplink load exceeds thethreshold, the present load is considered to be too high to initiatechannel state feedback transmission, and, thus, no uplink request isallowed to be transmitted at that occasion.

T0 conclude, with more efficient control channel handling, the totalavailable resources of a network can be more efficiently utilized,resulting in an improved network capacity.

Even though the invention has been described in relation to the conceptof LTE, it could be applied to any system that applies channel statefeedback reporting, such as e.g. CQI reporting, and scheduled uplink,such as e.g. WCDMA with enhanced uplink. The invention is, thus, notlimited to the disclosed embodiments, but is intended to cover variousmodifications within the scope of the appended claims.

What is claimed is:
 1. A method in a user equipment (UE) of reportingchannel state feedback from the UE to a base station, the methodcomprising the steps of: determining whether the UE has received anuplink grant from the base station; transmitting a first type of channelstate feedback information to the base station on a granted resourceupon determining that the UE has received an uplink grant, wherein thefirst type of channel state feedback information is a high-resolutiontype; and transmitting a second type of channel state feedbackinformation on a dedicated resource upon determining that the UE has notreceived an uplink grant, wherein said second type of channel statefeedback information is a low-resolution type, using a smaller number ofbits than the first, high-resolution type.
 2. The method according toclaim 1, further comprising the step of determining whether a channelstate feedback trigger criterion specified for said UE is valid andwherein the respective channel state feedback information is transmittedonly if said channel state feedback trigger criterion is valid.
 3. Themethod according to claim 1, wherein if the UE has no uplink grant thesecond, low-resolution type of channel state feedback information isperiodically transmitted while the first, high-resolution type ofchannel state feedback information is periodically transmitted if the UEdoes have an uplink grant.
 4. The method according to claim 1, furthercomprising the step of determining whether the UE has uplink data, andwhen the UE has uplink data and an uplink grant, a scheduled uplinktransmission comprises both channel state feedback information anduplink data.
 5. The method according to claim 1, further comprising thestep of determining whether the UE has uplink data, and when the UE hasan uplink grant but no uplink data, a scheduled uplink transmissioncomprises only channel state feedback information.
 6. The methodaccording to claim 5, wherein said scheduled uplink transmission isutilized as a signaling of an empty buffer status information to thebase station.
 7. The method according to claim 5, wherein said scheduleduplink transmission is utilized as an acknowledgement of the uplinkgrant that was transmitted in the downlink.
 8. The method according toclaim 1, wherein the type of report to be used for transmission of therespective channel state feedback information is dependent on the sizeof the received uplink grant.
 9. The method according to claim 8,further comprising the step of comparing the size of said uplink grantto a threshold (T1) and wherein the channel state feedback informationis transmitted in a report of a first type of a size associated with T1if said uplink grant size exceeds T1.
 10. The method according to claim9, wherein if said size does not exceed T1, said comparison is graduallyrepeated for one or more thresholds, T2 . . . Tn, wherein T1>T2>Tn andwherein a match results in the transmission of a report of an associatedsize.
 11. The method according to claim 1, wherein the size of theuplink grant is an indication of the bandwidth, the modulation size,and/or the code rate associated with the uplink grant.
 12. The methodaccording to claim 1, wherein remaining available energy for datatransmission is included on the uplink as a condition for transmissionof the channel state feedback information.
 13. A user equipment (UE) forproviding channel state feedback from the UE to a base station, the UEcomprising: a determining unit configured to determine whether the UEhas received an uplink grant from the base station; and a transmittingunit configured to transmit a first type of channel state feedbackinformation to the base station on the granted resource when the UE hasreceived an uplink grant, wherein the first type of channel statefeedback information is a high-resolution type, and a second type ofchannel state feedback information on a dedicated resource when the UEhas not received an uplink grant, wherein said second type of channelstate feedback information is a low-resolution type, using a smallernumber of bits than the first, high-resolution type.
 14. The UEaccording to claim 13, wherein said determining unit is furtherconfigured to determine whether a relevant channel state feedbacktrigger criterion specified for said UE is valid, and wherein saidtransmitting unit is configured to only transmit channel state feedbackinformation if the channel state feedback trigger criterion is valid.15. The UE according to claim 13, wherein the transmitting unit isconfigured to transmit the channel state feedback information in areport generated by a generating unit.
 16. The UE according to claim 15,wherein said generating unit is configured to periodically generate asecond, less detailed report type in case the UE has no uplink grant anda second, more detailed report type in case the UE does have an uplinkgrant.
 17. The UE according to claim 13, wherein said determining unitis configured to compare the size of said uplink grant to a threshold(T1) and wherein said generating unit is configured to generate a reportassociated with T1 if said size exceeds T1.
 18. The UE according toclaim 17, wherein if said size does not exceed T1, said determining unitis further configured to gradually repeat said comparison procedure forone or more additional thresholds, T2 . . . Tn, wherein T1>T2 . . . >Tn,and wherein said generating unit is configured to transmit a report ofan associated size when the associated size exceeds one of theadditional thresholds.
 19. The UE according to claim 13, wherein saiddetermining unit is configured to include remaining available energy fordata transmission on the uplink as a condition for generating saidreport.
 20. A method in a base station having a scheduler for obtainingchannel state feedback information from a user equipment (UE) the methodcomprising the steps of: determining whether channel state feedbackinformation is required; generating an uplink grant when channel statefeedback information is required; and providing the uplink grant to theUE when the uplink grant is generated in order to receive the channelstate feedback information on a granted resource; receiving a first typeof channel state feedback information on the granted resource when theuplink grant has been transmitted to the UE, wherein the first type ofchannel state feedback information is a high-resolution type; andreceiving a second type of channel state feedback information on adedicated resource when the uplink grant has not been transmitted to theUE, wherein the second type of channel state feedback information is alow-resolution type, using a smaller number of bits than the first,high-resolution type.
 21. The method according to claim 20, wherein saiddetermining step further comprises determining whether downlink data ispresent in the base station, and when downlink data is present,generating and providing the uplink grant to the UE in order to receivedownlink channel state feedback information on the granted resource. 22.The method according to claim 21, wherein said determining step furthercomprises determining whether an uplink load is below a threshold (T1)and when the uplink load is below said threshold, generating andproviding the uplink grant to the UE.
 23. The method according to claim20, wherein the uplink grant is provided to the UE for the purpose ofreceiving an uplink transmission on the granted resource containing atleast channel state feedback information, and wherein the uplinktransmission from the UE is used for estimating the uplink channelquality for link adaptation and/or channel dependent scheduling ofuplink data from the UE.
 24. The method according to claim 20, whereinan uplink grant is provided to the UE for the purpose of maintaininguplink synchronization.
 25. The method according to claim 20, whereinthe size of the uplink grant is variable.
 26. A base station comprisinga scheduler for obtaining channel state feedback information from a userequipment (UE) the base station comprising: a generating unit configuredto determine whether channel state feedback information is required, andto generate an uplink grant in order to receive channel state feedbackfrom the UE on a granted resource upon determining that channel statefeedback is required; a transmitting unit configured to transmit theuplink grant to the UE when the uplink grant is generated by thegenerating unit; and a receiving unit configured to receive channelstate feedback information, wherein the receiving unit is configured toreceive a first type of channel state feedback information on thegranted resource when the uplink grant has been transmitted to the UE,wherein the first type of channel state feedback information is ahigh-resolution type, and to receive a second type of channel statefeedback information on a dedicated resource when the uplink grant hasnot been transmitted to the UE, wherein the second type of channel statefeedback information is a low-resolution type, using a smaller number ofbits than the first, high-resolution type.
 27. The base stationaccording to claim 26, wherein said generating unit is furtherconfigured to provide an uplink grant to the UE in order to receivedownlink channel state feedback required for link adaptation and/orchannel dependent scheduling of downlink data to the UE on the grantedresource if the base station has downlink data.
 28. The base stationaccording to claim 27, wherein said generating unit is furtherconfigured to provide an uplink grant to the UE in case an uplink loadis also below a threshold (T1) such that uplink data from other UEs willnot be negatively affected.
 29. The base station according to claim 27,wherein said generating unit is further configured to provide an uplinkgrant to the UE in order to receive an uplink transmission on thegranted resource containing at least channel state feedback, and whereinsaid scheduler is configured to use the uplink transmission to estimatethe uplink channel quality for link adaptation and/or channel dependentscheduling of uplink data from the UE.
 30. The base station according toclaim 27, wherein said generating unit is configured to provide a UEwith an uplink grant for the purpose of maintaining uplinksynchronization.
 31. The base station according to claim 26, whereinsaid generating unit is configured to generate an uplink grant ofvariable size.